1. Field of the Invention
The present invention relates to a ventilating device for cooling a motor of a power driven tool such as a circular saw, a grinder and a screwdriver.
2. Description of the Prior Art
Conventionally, a ventilating device for cooling a motor of a power driven tool includes a fan driven by the motor disposed within a motor housing. The fan produces flow air which passes around the motor and goes out from an outlet formed in the motor housing or a gear housing positioned on the downstream side of the fan. Such an outlet includes a plurality of elliptical blow windows disposed in series in the rotational direction of the fan. However, when the air flows through the blow windows, air hurtling sounds of the fan may come out through the blow windows and blowing sounds of the cooling air may be produced, so that considerable unpleasant sounds may reach an operator. This may degrade the operation feeling of the tool. To this end, the prior art has proposed to provide partition walls which serve to separate the blow windows from each other such that each of the blow windows has a length in the blowing direction of the air to some extent.
However, the partition walls of the prior art blow windows have the same height with each other in the axial direction of the fan or in the radial direction with respect to the axis of the fan.
With this conventional ventilating device, the cooling air flows transversely of the blow windows at positions adjacent inlets of the blow windows, so that the pressure in the blow windows positioned rearwardly with respect to the rotational direction of the fan tends to become negative, resulting in that the air is sucked into the housing through the blow windows from the outside. For this reason, the cooling air may not be smoothly discharged and the amount of the discharged air is reduced. This may cause the problem that the cooling efficiency of the motor is degraded.
Additionally, since the air is sucked into the housing, such air flowing into the housing may collide with the air flowing transversely of the blow windows, so that a turbulent flow of the air is produced to produce collision sounds.
Further, due to the air flowing transversely of the blow windows, air hurtling sounds may be still produced at the blow windows. Furthermore, since the blow window positioned rearwardly with respect to the rotational direction of the fan has a smaller amount of discharge of the air than that positioned forwardly, a large amount of air flows through the blow window positioned in the frontmost position, so that blow sounds are produced by the air flowing through this blow window.
It is, accordingly, an object of the present invention to provide a ventilating device for cooling a motor of a rotary tool which provides sufficient amount of discharge of a cooling air for improving cooling efficiency of the motor and for improving the silentness of the fan.
It is another object of the present invention to provide such a ventilating device in which the air is dispersed to flow into blow windows by a small amount, respectively, so that the air can be efficiently discharged and that collision sounds, hurtling sounds and blowing sounds of the air can be reduced.